Congress President Sonia Gandhi will meet her party's toughest ally Mamata Banerjee this evening as she seeks to build consensus on the UPA's candidate for President. The Congress has so far not named its choice for the top post. However, Finance Minister Pranab Mukherjee is believed by many to be the front-runner among those vying to be the next President of the country. He cancelled an important trip to Afghanistan this week; his office says he wants to remain in Delhi to monitor the economic slowdown. But in political circles, his presence is being read as a sign that he is on stand-by for the Presidential nomination.